This invention relates to a turbine shroud segment attachment with a casing and several shroud segments arranged in the casing.
The use of shroud segments for sealing the gap at the tip of a rotor blade is known from the prior art. It is also known that the gap between the tip of the rotor blade and the shroud varies with the thermal expansion or contraction of both the rotor blade and the casing. An excessively large gap leads to flow losses, while an excessively small gap may cause mechanical damage.
Normally, the individual shroud segments are located loosely on the casing with appropriate clearance, with the clearance in the axial and circumferential direction being dimensioned such that it is irrelevant for the control of the running gap if the shroud segments expand under the influence of temperature. This arrangement provides that the radial location in the casing and, consequently, the radial gap to the rotor blade is largely independent of the temperature of the shroud segments.
Various solutions were proposed for the control of the gap between the tip of the rotor blade and the respective shroud segment. Specification U.S. Pat No. 4,657,479, for example, shows a mechanical solution with an active system in which the relative position of the shroud segment to the outer casing is variable. Control is effected by a multitude of bolts arranged between the shroud segments. The bolts are rotated by means of an actuating mechanism, separating the shroud segments from each other. This increases the entire circumferential length of the shroud composed of the individual shroud segments, resulting in a radial outward movement relative to the casing. Thus, the gap to the rotor blade tip is increased. Movement in the opposite direction is effected by spring-type elements.
This mechanism involves considerable complexity and manufacturing costs and is highly susceptible to malfunction. A further disadvantage is the need for an external control system.
A gap sealing arrangement is known from Specification DE 14 26 857 A1 in which the individual shroud segments engage each other on their circumferential sides in a labyrinth-type manner. This provides for a relatively large freedom of movement of the shroud segments, allowing the shroud segments to move freely during thermal contraction or expansion.
Specification DE 38 18 882 C2 describes a gas-turbine engine provided with shroud segments of chamfered design compensating for thermal contraction or expansion.
A further design is shown in Specification EP 0 381 895 A1. Here, the shroud is located with a radial gap allowing it to move radially and expand or contract under thermal influence.